1. Field of the Invention
The present invention relates generally to electrical switching apparatus and, more particularly, to a double-lever mechanism for the trip actuator of a circuit breaker. The invention also relates to trip actuator assemblies having double-lever mechanisms and to circuit breakers with trip actuators employing double-lever mechanisms.
2. Background Information
Electrical switching apparatus, such as molded case circuit breakers, generally include at least one pair of separable contacts which are operated either manually, by way of a handle disposed on the outside of the case, or automatically by way of a trip unit in response to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition.
One type of molded case circuit breaker trip unit, known as a Flux Transfer Shunt Trip (FTST) unit 2, is shown in FIG. 1. Trip units such as the FTST unit 2 generally include an enclosure 4 housing a coil and plunger assembly 6. The coil and plunger assembly 6 includes a coil 8 which is energized in preparation for moving a plunger 10. For example, the plunger 10 may be spring-biased, being held against such spring-bias by a pivotal trip lever 12 or, as in the case of the FTST unit 2, the assembly 6 may be electrically charged, with the coil 8 operating to extend the plunger 10 in response to an electrical signal received as the result of the overcurrent condition. The pivotal lever 12 is pivotally connected to the enclosure 4 by a pivot member 14. In response to the overcurrent condition, the trip actuator plunger 10 is fired, or otherwise released, from its biased or charged, unextended position, such that it extends and engages the pivotal trip lever 12 causing it to rotate and engage the trip bar (not shown) of the circuit breaker (not shown). The circuit breaker trip bar then rotates thereby tripping open the circuit breaker separable contacts (not shown).
As shown, the pivotal trip lever 12 is relatively short with the distance between the pivot 14 at one end of the lever 12 and the other end of the lever 12, at which point the plunger 10 acts upon the lever 12, being relatively small. Such a design is mechanically inefficient, requiring a larger coil and plunger assembly 6 than necessary, in order to provide the requisite force and plunger stroke to engage and actuate the circuit breaker trip bar.
In view of the foregoing, it is desirable to provide a trip actuator assembly which is more efficient, requiring less force to actuate and thus reducing the size of the coil and plunger assembly components necessary to effectuate such force. It is also desirable that the improved trip actuator assembly be readily interchangeable with a variety of electrical switching apparatus, including molded case circuit breakers.
There is, therefore, room for improvement in trip actuator mechanisms for circuit breakers and in circuit breakers employing trip actuator mechanisms.